10 things you didn’t know about leeches

Poor leeches. They get a bad reputation for being nothing but slimy, oozy, hysterics-worthy bloodsuckers—and while they may be all those things, leeches are actually pretty cool once you get to know them.

From a distance. On dry land. Not stuck all over your legs.

Here are a few things you might not have know about these creepy crawlies.

1. Leeches are actually worms

Yup. Leeches have a lot in common with your everyday earthworm—but there are some important differences. Leeches’ bodies are much more solid than earthworms’, and while they show some external segmentation, the divisions on the outside don’t match up with how organs are arranged on the inside. Plus, there’s that whole bloodsucking thing. But, like earthworms, leeches make great bait, especially for walleye.

2. Not all leeches suck blood

Blood-eating leeches are only one type, although they’re the ones we most often notice, mostly as we’re dancing around trying to rip them off our legs. Many freshwater leeches, in fact, don’t eat blood at all—they’re carnivores, but they stick to molluscs, insect larvae, and worms. Even those that do drink blood aren’t actively looking for human blood—they prefer frogs, snails, turtles, and other aquatic creatures. But hey—a meal’s a meal, and if someone’s ankle presents itself, it’s nom time.

3. Leeches are hermaphrodites

Leeches have both male and female reproductive organs, but that doesn’t mean they can do it all themselves, fertilization-wise. Instead, leeches line themselves up, head to feet—or as close as a leech gets to a head, or feet—and trade sperm packets. Not quite a romantic weekend in Niagara Falls, but it does the trick.

4. Leeches are everywhere

You’re never going to escape them, so you might as well learn to appreciate them. Leeches are found on pretty much every continent—and while there are no freshwater leeches in Antarctica, you can find the little suckers floating in every ocean in the world.

5. Leeches can get really big

One species found in the Amazon can grow up to 45 centimetres long—with a proboscis (nose) that can grow up to half a foot in length. Fortunately, most of the species found in Canada aren’t quite so horrifyingly massive—the bloodsucking species we’re familiar with, Macrobdella decora, only grows up to 10 cm or so.

6. Leeches are used in medicine

No, not for old-fashioned bloodletting—that went out of style with the corset and the bustle. Instead, doctors use leeches and their blood-clot-busting saliva to help drain blood from swollen areas following reconstructive surgery—especially small areas with lots of blood vessels like ears, fingers, and toes, where blood clots can easily form. And although the science is still a little fuzzy, researchers in Germany are also using leeches to help with the pain of osteoarthritis.

7. Leeches can’t hear, and they don’t see much

Leeches don’t have ears, although they can sense vibrations through their skin, and they can’t see much beyond how bright a light is. Instead, they use a strong sense of taste and touch to communicate chemically and physically with each other.

8. Leeches adapt well to tough conditions

Some species can go a year without food, and they tend to tolerate low levels of oxygen well. Also, some species seem to do just fine in areas with high levels of pollution.

9. If a leech is stuck to you, just wait it out

If you get out of the water and you’ve got a leech stuck to you, the best—although not the easiest—thing to do is simply wait for it to finish eating, at which point it will drop off and go on its merry way. If you can’t get over the ick factor, though, a little salt sprinkled on the leech will cause it enough discomfort to get it to drop off early.

10. Leeches eat a lot, relatively speaking

You’re definitely not going to die from a leech bite, but they are capable of eating up to five times their body weight in blood. Conveniently, they can store excess nutrients for later use, just in case pickings get slim in the blood department.

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